The present invention relates to oil field tubular goods and here particularly to fluid tight joints between, for example, a box or sleeve member and a pin member of drill pipe with weld-on tool joint.
Joints of the type to which the invention pertains are, for example, provided with a polytetrafluoroethylane ring which is disposed in a groove and seals the two members against each other and particularly the interior of the two members against the common exterior. The ring used fills the groove completely so that particularly upon threading the two members into each other a gas and liquid tight seal is obtained. A seal and joint in accordance with the general principles outlined above is for example disclosed in German printed patent application No. 11 29 125. Herein a groove is provided in the essentially cylindrical surface of the sleeve part of the joint. Also, French Pat. No. 13 60 257 suggests to provide such a resilient sealing element in a groove which is disposed in a radial shoulder of the joining sleeves.
It was found that sealing constructions in accordance with the known principles requires supplemental and additional expenditure for making the joint as compared with the joints of the type in which a metal-to-metal seal is employed. On the other hand, metal-to-metal seals require a very high degree of accuracy and close tolerances as far as machining the relevant portions in the sleeve as well as in the pin member is concerned. Still, the last mentioned pipes of joints are favored. Particular criterium in the metal-to-metal seal type joints is the relative sensitivity of the pin member and here particularly of the outer sealing surfaces being located right at the end of the pin. When exposed, they can easily be damaged, particularly during transportation and in the case of inept installations. Also, it has to be considered that making up of a joint is usually carried out with one member being inserted in the bore hole and another one is suspended above by means of an oil derrick. The freely suspended casing may well begin to swing and the pin member end may hit some part and be damaged. As to sealed casing joints see also U.S. Pat. Nos. 2,907,589; 3,667,784; 3,100,656; 3,489,438 and German Pat. No. 600537.